Synthetic polyester yarns have been known and used commercially for several decades, having been first suggested by W. H. Carothers, U.S. Pat. No. 2,071,251, and then by Whinfield and Dickson, U.S. Pat. No. 2,465,319. The polyester yarns that have been manufactured and used hitherto have constituted essentially two general categories, (1) spun yarns of cut or staple fiber twisted together like cotton, for example and (2) multi-filament yarns. This application is not concerned with yarns spun only from cut fiber, such as are covered in copending application Ser. No. 07/420,457, filed simultaneously herewith, but with filament yarns, i.e. yarns of category (2) comprising continuous filaments, which themselves presently constitute two further categories, (a) undrawn yarns, which have been mainly draw-texturing feed yarns (often termed POY) that are further processed (DTFY is draw-textured) because their properties are not yet suitable to permit use in forming most fabrics, and (B) drawn yarns. This application is concerned only with multi-filament yarns of category (B), i.e. drawn yarns, that are suitable for use directly in fabric construction, e.g. by knitting or weaving. These yarns do not need a preliminary treatment to change important filamentary characteristics, such as modulus, because these yarns have already been drawn by a conventional process to increase their modulus. Such drawn yarns fall into essentially two categories, according to their method of preparation. In the 1950's, drawn polyester filament yarns were made commercially only by a split process, involving first melt-spinning (i.e. extruding molten polyester into solid filaments) at a relatively low (withdrawal and wind-up) speed to make an unstable undrawn yarn of low orientation that was wound onto a package, and then this package of undrawn yarn was unwound and subjected to a separate drawing operation to increase orientation and crystallinity and thereby make stable yarns of low shrinkage that could be used in textile operations, such as weaving and knitting. This process is called the split process to distinguish from the later coupled process, in which the two separate steps of spinning and drawing are combined into a continuous process, i.e. without intermediate wind-up, as disclosed, e.g. by Chantry et al. in U.S. Pat. No. 3,216,187. The coupled spin-draw process has been used by Du Pont on a commercial scale for more than 20 years with high speed winders capable of operation at speeds of 3-4 km/min, and we consider it far preferable over the older split process for technical reasons, but the split process may still be operated in some parts of the world. The coupled process produces more uniform products, because the unstable undrawn yarn is immediately drawn, without time for significant change in properties, and because all portions of each yarn have an identical history. In recent years, it has been shown that the original coupled process can be modified by increasing the speed of withdrawal of undrawn filaments, with the result that even the undrawn intermediate filaments (that are not wound-up) are stable to heat, for example.
Drawn polyester multi-filament yarn has been recognized as having significant advantages over cotton yarns in some respects, for instance its thermoplastic characteristics that enable polyester-containing fabrics to hold their shape, for instance a crease, and to have wash-wear characteristics, its low cost of manufacture, its uniformity, its superior strength, and its resistance to degradation. However, hitherto, some people have expressed a preference for wearing garments from cotton fibers because of attributes that can be summarized as "comfort", to the extent that there has been a trend recently towards using more 100% cotton fabrics, despite the practical advantages of wash-wear 100% polyester fabrics. Because of the sophistication of the textile industry, both of the polyester fiber manufacturing industry and of downstream consumers of textiles, and because of the commercial interest in providing apparel and fabrics that will perform well during actual use by the ultimate consumer (wearer), much attention has been devoted to analyzing appropriate requirements. Many technical papers, for example, have been published on various aspects, and patents have been issued with the objective of improving the "comfort" that can be obtained from textile articles, and their constituents, and the literature has been replete with these suggestions for several years. So it has long been considered desirable to improve various properties of textiles prepared from drawn multi-filament polyester yarns, and much effort has been devoted in the textile industry towards this objective.
An important objective of our invention is to provide such polyester drawn multi-filament feed yarns and filaments in a new form, which can be formed into fabrics and garments that can show improved moisture-wicking properties, as discussed herein.
Polyester filaments are characterized by their extreme hydrophobic character, as mentioned in "Polyester Fibres--Chemistry and Technology", by H. Ludewig--English translation 1971--John Wiley and Sons, Ltd., in Section 11.1.5 on pages 377-378, and also in Section 11.4 on dyeing properties, starting on page 398. Indeed, the difficulty of dyeing polyester yarns and fabrics is notorious. Ludewig's book mentions many aspects of polyester fibers and their preparation and properties.
It is conventional to coat all freshly-extruded filaments with a "finish", which is generally an aqueous emulsion comprising a lubricant and an antistat. Finishes are discussed briefly in Section 5.5, starting on page 193, of Ludewig, referred to above. As mentioned on page 195, the literature reveals relatively little about the compositions of the spin-finishes that are actually used. Although there is now considerable patent and other literature, the precise finish formulations are generally closely-guarded secrets by the yarn manufacturers, and different compositions are formulated for different purposes, depending on the particular intended processing and possible specific requests by individual customers, and these formulations change, sometimes quite frequently. As will be related hereinafter, a dramatic change in the surface properties of the filaments of the eventual drawn yarns, and of articles containing them, such as fabrics and garments, may be obtained by a relatively simple modification to the spin-finish that is applied to the freshly-extruded polyester undrawn filaments. Conventionally, the spin-finish is the first contact that a freshly-extruded filament encounters after solidification. The finish was generally applied by a finish roll, rotating in a bath of the finish, so that the filaments pass through the finish emulsion as they brush past the finish roll on their way from the solidification zone to the feed roll that determines the withdrawal speed from the spinneret. Before the finish roll, it is generally desirable to avoid or minimize contact between the filaments and solid objects, and so the only other closely-adjoining solid objects are generally guides that are intended to confine the filaments before contacting the finish roll. A finish roll is not the only method of applying finish, and other methods have been used and suggested, including spraying or metering the finish onto the filaments.